1. Field of the Invention
The present invention relates to a video coding-decoding (CODEC) method and an apparatus therefor, and more particularly, to a video CODEC method in an error resilient mode and an apparatus therefor. Also, the present application is based on US Provisional Patent Application No. 60/067,013, entitled “Video CODEC Method in Error Resilient Mode”, by the present applicant.
2. Description of the Related Art
In general, in case that an error exists in a channel, video CODEC cannot cope with error of the channel when encoding all frames into bit streams. This is because the bit streams have no decision element for determination of whether streams have no decision element for determination of whether to restore or discard the error region. Thus, it is difficult to determine whether a certain portion of a frame has bit loss by an error, or whether the entire frame has an error, so that there is a problem that a start point of the bit stream should be searched in the next frame, ignoring the coded bit stream of the entire frame. In a conventional CODEC, an additional device is used as the decision element in order to solve such problem. As an example, according to the CODEC defined in the H.263 standard, a picture start code (PSC) is employed and if an error is detected after this field information, the region following the PSC is ignored and the next PSC is then searched. Further, a group of block start code (GBSC) indicating the start of the group of block (GOB) is employed and if an error is detected after this information, only the corresponding block of the GBSC is ignored and then the next GOB is searched, thereby reducing the amount of the ignored region.
FIG. 1 shows an example of a video data packet generated by a conventional CODEC in an error resilient mode. The video data packet of FIG. 1 is an example of the video data packet generated in the MPEG-4 CODEC. Referring to this packet, in the conventional error resilient CODEC, data is divided into motion data and texture data for coding. The motion data consists of a macro block identification bit (COD) indicating whether or not coding is performed, a macro block pattern chrominance (MCBPC) bit indicating the chrominance of each macro block and a motion vector, and the texture data consists of coded block pattern luminance (CBPY) data, data quantization (DQUANT) data and discrete cosine transform (DCT) data. Such motion data and texture data are divided by a motion marker (MM). Also, the DCT data is coded by reversible variable length coding (RVLC).
The decoding process of the bit stream coded in the above manner will be described. First, a resync marker RM is searched in the bit stream. If an RM is found, information up to the next RM is regarded as one packet. A motion vector data part (MVDP) consisting of motion vectors has only predicted motion vectors, so that it is possible to use an actual motion vector only when the previously decoded motion vector exists. Thus, if an error is detected from the MVDP of the bit stream, the corresponding entire packet is ignored, and an RM corresponding to the next packet is searched for decoding, thereby causing loss of a large amount of information.